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21:04, EEST
May 10, 2018
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I’m dealing with some inconsistent publish response behavior. Our subscription is setup for Publish responses to come in at 1 minute intervals, which we’ve verified is what the UA server (kepware running on a different computer) is doing. Instead the subscription listener is receiving several publish responses at once every few minutes, followed sometimes by a regularly scheduled 1 minute publish response, then another gap of 3 to 4 minutes. Eventually the subscription listener stops receiving anything at all. This behavior only happens on a test environment running 14.04 ubuntu in an isolated network environment, and I noticed recently that the RTC on the linux box is terribly inaccurate running a few minutes ahead, and manually corrected the time (the kepware server had an accurate time). This resolved all issues and published responses came in on 1-minute intervals like clockwork. Does anyone know if system time inconsistencies could cause issues with subscription publish reponses?
15:52, EEST
April 17, 2013
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Hi,
System time being slightly ahead should not cause problems in subscriptions.
Basically the OPC UA subscriptions work so that notification messages are only sent when there’s data changes to notify (there’s also a mechanism for sending an empty message once in a while as a keep-alive). So the most straightforward explanation would be that the server just doesn’t have anything to report and for this reason it doesn’t send notifications for some time.
So, the question is: how did you verify that the server is sending the publish responses every minute?
To proceed further, it would be beneficial to see a log file which shows the incoming publish responses as well as the evidence that SubscriptionNotificationListeners are not called for these value changes. The log file of incoming OPC UA messages can be prepared with Wirehark (https://prosysopc.com/blog/opc-ua-wireshark/) and your application level log showing the inconsistent listener calls should provide enough information. Files cannot be attached here to the forum, so please send these files to us by email at uajava-support prosysopc.com
18:07, EEST
May 10, 2018
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I’ll send the wireshark logs, but I can confirm that the publish responses are firing off every minute. The UA server is a kepware installation connecting to an OPC classic simulator which is updating it’s values at a predetermined interval. In short, there is no 1-minute interval where there isn’t an update to the subscribed nodes and I have confirmed that publish requests are being sent to the ua client (with the prosys sdk) on schedule. Changing the system clock does have an effect on the processing of publish requests, I’ve been able to reproduce the effect by changing the system clock on the client by as little as one second.
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